The present invention relates to novel acrylic synthetic fibers having high flame retardancy and outstanding gloss and transparency.
While so-called modacrylic fibers comprising a relatively large amount of copolymerized vinyl halide are flame-retardant to some extent in themselves, it is desired to provide more flame-retardant fibers to meet the rapidly increasing needs of the community for flame retardancy which are urged, for example, by recent hotel fires. Flame retardancy is imparted to fibers by copolymerizing a flame-retardant monomer with a material for forming fibers, by admixing a flame retardant to a spinning solution and spinning the mixture, by depositing a flame retardant on fibers by aftertreatment, and by other methods. Of these methods, it is general practice to admix a flame retardant with a spinning solution because this method gives semi-permanent flame retardancy to the fiber without greatly impairing the original properties of the fiber. Various flame retardants are known which include halides containing chlorine, bromine or the like, compounds containing nitrogen and phosphorus, and metal compounds, but only a few of them are effective for giving flame retardancy to acrylic synthetic fibers. Of these, tin oxide, antimony oxide, magnesium oxide and like metal oxides are relatively useful for imparting flame retardancy to acrylic synthetic fibers, whereas these oxides have the drawback of being insoluble in solvents and therefore giving only fibers which are very low in transparency and have an impaired quality. Such metal oxides have another drawback of requiring an increased pressure for filtering the spinning solution and being liable to clog up the nozzle in the course of fiber making process. Thus, it is extremetly difficult to develop acrylic synthetic fibers which are highly flame-retardant and satisfactory in both gloss and transparency.